Canine Mammary Cysts

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Much like women, your female dog can be affected by a variety of diseases of the mammary, or breast, tissue. These diseases include infection, inflammation, benign growths or malignant cancer of one or more mammary glands. Also known as fibrocystic disease, benign mammary cysts result when the ducts of the mammary gland are expanded and become filled with fluid, causing masses or lumps to appear in one or more mammary glands. Since several of these diseases can cause similar lumps, it is important to differentiate this benign condition from more serious conditions that can affect the mammary glands.



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Mammary cysts may affect any age or breed of dog, although they are most commonly seen in middle-aged to older female dogs. Dogs with mammary cysts may have small raised nodules present in one or more mammary glands, or they may have flat, rubbery masses present. The skin over the cyst may appear blue, gaining this condition the nickname "blue dome cysts." If the cysts become large enough, they can rupture, releasing a greenish-brown or clear fluid. It is possible for ruptured cysts to become inflamed or even infected, which may require evaluation and treatment by your veterinarian.



The development of mammary cysts is often related to natural hormone levels in the body, and therefore cysts can appear or regress depending on the phase of your dog's estrous (heat) cycle. Cysts often appear and grow rapidly (possibly to the point of rupturing) during the time that your dog is in heat, and then regress once the heat cycle is over. Not all mammary cysts appear because of the heat cycle, and therefore may not regress with phases of the cycle. Mammary cysts are also often diagnosed in dogs who receive artificial hormones to suppress their heat cycles, particularly the hormone medroxyprogesterone (Provera).



Although examination of affected mammary tissue may show lesions consistent with mammary cysts, the only way to confirm the diagnosis is by biopsy. Cysts can resemble other benign or malignant mammary conditions, so it is important to differentiate them from a potentially more serious condition. Mammary cysts and tumors are often found together, so if your dog is diagnosed with cysts, she should also be evaluated for the presence of mammary cancer.



Mammary cysts are benign and therefore treatment may not be required. However, it is unknown if the presence of cysts makes your dog more likely to develop mammary cancer, so your vet may suggest removal of the cysts to ensure none of the lesions become cancerous. If your dog develops cysts that grow and then regress based on her heat cycle, consider spaying her to eliminate the hormonal influence. Overall, successful treatment of this disease results in an excellent prognosis and no long-term health effects.


By Amanda Fulmer

Canine and Feline Cytology: A Color Atlas and Interpretation Guide; Rose Raskin and Denny Meyer
United States Kerry Blue Terrier Club: Mammary Disorders of the Bitch


About the Author
Amanda Fulmer is a veterinarian in Greenville, S.C. who earned specialty certification in medical oncology in 2008. She received a veterinary degree and advanced oncology training from Louisiana State University. Her scientific research has been published in several professional veterinary journals. She also lectures around the country on various topics in her field.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.


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